Current limiting lightning arrester with porous gap structure



p 1954 E. w.' STETSON CURRENT LIMITING LIGHTN ETAL ING ARRESTER WITH POROUS GAP STRUCTURE 2 Sheets-Sheet 1 Filed Dec. 2'7, 1961 p 9 1 E. w. 'STETSON AL 3,151,273

CURRENT LIMITING LIGHTN AR TER WITH POROUS GAP STRUCTUR 2 Sheets-Sheet 2 Filed Dec. 27, 1961 b 550 w'oo 15'00 zo'o'o zs'oo 3600 Ebr/ W 5/6).5072,

United States Patent 3,151,273 CURRENT LIMITING LIGHTNING ARRESTER WITH POROUS GAP STRUCTURE Earl W. Stetson and James H. Snell, Jr., Pittsfield,Mass., assignors to GeneralElectric Company, a corporation of New York Filed Dec. 27, 1961, Ser. No. 162,382 Claims. (Cl. 315-36) This invention relates to a lightning arrester and, more particularly, to a current limiting lightning arrester having a porous gap structure.

In the lightning arrester field, the use of some type of spark gap construction in series with a type of nonlinear resistance valve material is well known. The combination of the gaps and valve material is utilized to provide a path to ground for transient and surge voltages which may appear on an electrical conductor, Where such voltages would be of sufficient amplitude or strength to damage electrical equipment connected to the conductor. As is well known, the valve material presents a high resistance to the low voltages of the normal power line and lower resistance to the higher voltages, such as surge voltages, which the arrester is designed to conduct to ground to prevent damaging the electrical equipment connected to such power line. The gaps in general are over at a predetermined voltage level. This predetermined voltage level is the limit of transient or surge voltages which can be carried by the electrical conductor without damage to electrical equipment. In the normal construction of these arresters, the arc within the gaps is caused to move into an arcing chamber associated with the gaps, to thereby increase the arc voltage. Of course, the main object of the arrester is to discharge these sudden surges, which may be lightning or switching surges. Obviously, after the surge has been dissipated it is desired that the arrester return to its open circuit condition to prevent the discharge of the normal line current, which is usually termed the power follow current, by the lightning arrester.

In the operation of lightning arresters, after the sudden surge has been discharged, the arcs are lengthened to thereby increase the arc voltage, which will limit the power follow current which flows in the lightning arrester. It will be clear that the greater the resistance of the are that is maintained in the arcing chambers, the greater will be the voltage drop across such arcs. Clearly, the larger the chamber the longer will be the arc and thus the greater will be the arc voltage. However, it is desirable to provide a high are voltage, while at the same time maintaining an arrester which is of sufficiently small size that it may be readily installed on an electrical power line near electrical equipment which requires protection from voltage surges.

It is, therefore, one object of this invention to increase the arc voltage within an arcing chamber without increasing the size of such arcing chamber. a

It is a further object of this invention to improve the efficiency of a lightning arrester without increasing the size or cost of such arrester.

A still further object of this invention is to provide a new and improved spark gap structure which will provide greater are voltages without increasing the size or cost of such structure.

Another object of this invention is to provide a spark gap assembly which will more rapidly build up are voltages within such assembly as compared to presently avail able spark gap assemblies.

Another object of this invention is to provide a gap structure which will increase the arc current which can be moved1'into the arc chamber.

It is still another object of this invention to provide an improved lightning arrester with a novel are gap structure whereby the arrester will be able to efficiently. dissipate voltage surges which may be experienced on the electrical conductor connected to such lightning arrester.

In many present day lightning arrester structures, a coil is provided in series with the sparking gap, such that when the coil is energized a flux is created which will aid in moving the arcs from the gap into the arcing chambers. One construction of such a coil is shown in Patent No. 2,566,895, issued September 4, 1951 to J. W. Kalb for Protective Device and assigned to the same assignee as this invention. As is well understood by those skilled in the art, these coils are generally shunted, either with a resistor or a gap, as a voltage limiting element to protect the coil from flashover and insulation damage due to the large voltage surges. In general, it has been found that it is more desirable to use a gap to shunt the coil. As will be understood, the impulse current flowing in a gapprovides practically negligible voltage drop, while, if a resistor is utilized as a shunting element, a comparatively large drop is obtained, which must be considered in determining the overall protective characteristics of the arrester. Of course, it will be obvious that, in general, the cost of a gap for shunting of a coil is less than the cost of a resistor. One problem which has been found in use of shunting gaps is providing a sufficiently rapid build up of flux in the coil to cause the desired arc movement within the coil gap and the main gaps to thereby provide the desired current limiting action of the arrester. By use of a proper arc chamber with the coil shunting gap, it has been found possible to rapidly transfer a sufiicient amount of current from the gap to the coil to obtain the desired current limiting effect. This has been possible due to a novel arc chamber of the coil shunting gap which rapidly increases the voltage within such coil shunting gap, to thereby cause a sufiicient amount of current to flow through the parallel coil. The impedance of the coil is so designed that after the voltage has built up in the shunting gap, current will be transferred to the coil.

It is therefore a further object of this invention to provide a coil shunting gap which will provide substantial voltage increase in the are so as to transfer the current from the are within the gap to the coil in order to obtain a flux to move the arc in the coil gap and in the associated main gaps.

Other problems which are generally found in the use of gaps in lightning arresters and the like are related to the are sticking in the gap, and the restriking of the arc during the current limiting operation. If the arc sticks in its initial position it will burn back the electrodes, thus altering the sparkover characteristics of the spark gap and possibly resulting in arrester failure. When the arc restrikes there is danger of the gap losing necessary control in the interruption of the power follow current. Such restriking can also lead to the are sticking in the gap. Both of these problems are related to the flux in the coil and the rate at which the flux is developed in the coil.

Thus, a further object of the invention is to provide a coil shunting gap which transfers the current from the gap to the coil in a manner so as to obtain a relatively restrike-free operation of the gaps in the arrester.

A further object of the invention is to provide gaps, both main gaps and in the coil shunting gaps, which have a current loop therein, which will aid in moving the are within the gap to prevent the arc sticking in its initial striking position.

In carrying out this invention in one form, a spark gap construction is provided comprising a pair of electrodes fixed in an arc chamber. The are chamber is formed entirely of a porous material which aids in increasing the arc voltage. Further, the electrodes are formed to provide a current loop therein to aid in moving the are which strikes between the electrodes. A coil is provided in parallel circuit relation with one gap, the coil having an impedance such that as the voltage of the arc within the gap increases the current flowing therethrough is transferred to the coil in order to develop a flux for moving the arc in the gaps.

In a lightning arrester made according to this invention, the gaps, including the main gaps and the coil shunting gap, are connected electrically in series with a non-linear resistance material so as to provide a lightning arrester which will substantially limit the current flow therethrough.

The invention which is desired to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its objects and advantages are obtained, as well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment thereof when considered in the light of the accompanying drawings, in which:

FIGURE 1 is an elevation view, partially in section, of one form of a lightning arrester made according to this invention;

FIGURE 2 is a perspective view, partly in section, showing one form of the novel spark gap assembly made according to this invention;

FIGURE 3 is a top view, with portions broken away, of the spark gap assembly shown in FIG. 2;

FIGURE 4 is an elevation view with parts shown in phantom of the spark gap assembly taken on the line 44 of FIG. 3;

FIGURE 5 is an exploded perspective view of a main gap structure according to one form of this invention, such as one of the gaps of FIG. 4;

FIGURE 6 is an exploded perspective view of a coil and coil shunting gap structure made according to one form of this invention, such as the coil and coil shunting gap structure of FIG. 4; and

FIGURE 7 is a graph comparing the build up of arc voltages within a gap structure made according to this invention and a prior art gap structure.

Referring now to the drawings, in which like numerals are used to indicate like parts throughout the various views thereof, and in particular with reference to FIG. 1, there is shown a lightning arrester 10. Arrester it) comprises an annular, insulated outer member or casing 12 which may be for example, porcelain or the like, having an upper electrode or terminal 14 shown as connected to a line electrical conductor 16, and having a lower electrode or terminal 18 connected to ground, as indicated. The upper terminal 14 is preferably a metallic member which is sealed to an opening within the casing 12 in any desired manner such as, for example, the sealing resin 20, and is provided with a lower portion 22 which extends into the hollow interior of the casing 12. Within the outer member or casing 12 is mounted the component parts of the lightning arrester comprising the main gaps in series and the coil and coil shunting gap in series with the main gaps, these series gaps being generally indicated as 24, and a non-linear resistant valve material indicated at 26. A spring member 23 makes a firm electrical connection between the lower portion 22 of the terminal 14 and an upper metallic plate 3% which is mounted on the gap assembly 24. A lower plate 32 between gap assembly 24 and the non-linear valve-resistant material 26 form an electrical connection between the gap assembly 24- and the valve material 2.6. The lower end of valve material 26 is firmly seated on and makes electrical contact with a lower metallic member 34, which is in electrical contact with the bottom closure member 36. The terminal member 18 is electrically connected to member 36. As indicated, the member 34 is firmly held against the lower end of the casing 12 by member 36 and is provided with a sealing means, such as resin 38, to form a tight hermetic seal between the lower member 34 and the casing 12. The outerclosure member 36 is firmly secured to the sides of the casing 12 in any desired manner, for example, as indicated by the peened over portions of the member '56.

Thus there is provide a lightning arrester 10 which is connected between a line conductor 16 and ground. A sudden lightning surge appearing on the line conductor 16 will cause the spark gap assembly 24 to are over, allowing the current to flow through the valve member 26 and the lower terminal l? to ground. As is well understood, after the power surge had been dissipated the follow current, which then flows within the lightning arrester ltl, will be interrupted by the interaction of the spark gap assembly 24 and the valve member 26. The construction and operation of the spark gap assembly 24 is discussed in more detail in the following description.

Referring now to FIG. 2 of the drawing, a preferred embodiment of a spark gap assembly is shown in detail as spark gap assembly 24 comprising an upper terminal plate 31? and a lower termianl plate 32 which are serially connected by rivets to the electrodes of the spark gaps in a manner hereinafter described. The main body of the spark gap assembly 24 comprises a number of blocks of porous material which make up the various spark gap chambers for the spark gap electrodes within the spark gap assembly 24. A coil member 42 is provided, substantially within the center portion of the spark gap assembly 2.4 and is serially connected with the upper and lower spark gap electrodes so as to be energized by the current flowing therethrough to provide the desired magnetic flux to cause movement of the arc from the spark gap electrodes into the spark gap chambers in a manner to be described hereinafter.

it has been discovered that by use of a porous plate material to form the spark gap chambers that a higher rate of increase in the arc voltage is obtained as the arc proceeds along the spark gap electrodes and progresses outwardly onto their running surfaces This is highly desirable in a current limiting arrester since it is the basic means whereby the follow current is kept low and is interrupted each time the arrester is called upon to opcrate. Of course, this in turn will permit the minimizing of the amount of the non-linear valve material necessary in the arrester, and will thereby permit lower IR voltages than would be possible with non-current limiting arresters.

The graph of FIG. 7 shows the substantially higher voltage increase that is possible by using a porous material for the arcing chamber rather than the impervious material of the prior art. In FIG. 7 the lower curve shows the increase in are voltage with respect to time of a spark gap or arcing chamber using impervious material. The test was performed using a magnetic field to move the are from between the electrodes into the arc chamber, using a test current of 1,000 amps. A second test was performed using the identical conditions, the only difference being that the arcing chamber was made of porous material. The upper curve shows the results of this test. As can be seen, in less than 300 microseconds, the gap using a porous arc chamber had an arc voltage of 2,000 volts while the gap using an impervious arc chamber did not reach more than 600 volts in a similar period.

It has further been discovered that with a given magnetic field strength, the maximum arc current which can be moved out of the restricted part of the gap electrodes and into the arc chamber is much higher for are chambers which are made of porous material. This also is an important consideration in the design of current limiting arresters, inasmuch as the arresters' may be applied to power lines which have high available currents. The amount of non-linear resistance valve material may be kept to a minimum, and yet ensure that the initial curw rent will move out of the restricted portion of the spark gap electrodes by the use of porous material to form the arcing chambers. This is particularly shown by the following test results which set forth the currents at which the arc was stuck in the striking position within the electrodes. In the first test, the plates of the arcing chamber were made of impervious material, while in the second test the plates were made of a porous structure. The tests were performed with electrodes having ditferent radii. In one series of tests the electrodes provides had a radius of A; of an inch while in the second series of tests the electrodes had a radius of /2". The test results are as follows:

Electrode l5 Electrode Type Radius, Radius,

amps. amps.

Both gap plates impervious 450 800 All porous structure 1, 600 1, 600

It should be noted that the above tests, where the all porous structure was utilized, the maximum arc current used in the tests was 1600 amps. Therefore, it should be noted that, although 1600 amps. is listed in the above table, the arc did not actually stick in the starting position between the electrodes but was moved out of the electrodes and into the arc chamber. It is believed that the above test results substantially indicate the improved results which are obtained by use of the porous arcing chambers of this invention.

Reference will now be made to FIGS. 3, 4, 5, and 6 for a detailed description of a preferred embodiment of the spark gap assembly of this invention. In FIGS. 3 and 4 the spark gap assembly 24 is shown. In FIG. 3 there is shown the top plate 30, broken away at one end thereof, to show the first pair of spark gap electrodes 44 and 46. As shown, spark gap electrode 44 is connected by rivet 48 to the upper plate 30. The spark gap electrode 46 is connected by a rivet 50 to the first of the spark gap electrodes in the coil shunting gap, shown more in detail in FIG. 6. A third rivet 52, see FIGS. 4 and 6, connects the second electrode of the coil shunting gap electrodes to the first electrode of the lower spark gap, while the second electrode of the lower spark gap assembly is connected by a rivet 54 to the lower plate 32 of the spark gap assembly 24. Further, as shown more particularly in FIG. 6, the inner end 56 of coil 42 is connected to the lower electrode 58 of the coil shunting gap, while the outer end 60 of the coil 42 is connected to the upper electrode 46 which in turn is connected by rivet 50 to the second electrode 62 of the coil shunting gap. From this it can be seen that the coil 42 is connected in parallel circuit relation with the coil shunting gap which comprises the electrodes 58 and 62, while both the coil 42 and the coil shunting gap comprising the electrodes 58 and 62 are connected in series circuit relation with the upper gap and the lower gap. In this manner, the coil shunting gap electrodes 58 and 62 will are over when subjected to a high surge voltage, such as lightning or a switching surge so as to shunt the coil 42. However, due to the design of the coil shunting electrodes 58 and 62 the arc struck between the electrodes will be caused to move out into the arcing chamber 64 which is formed in the porous disks 66 and 68. The voltage of the arc will rapidly increase, thereby causing the current to flow within the coil 42, to thereby provide additional flux to move the arcs in the main gaps and in the coil gap out into the arcing chambers to thereby increase their voltages.

Referring now to FIG. 5 of the drawing, the upper spark gap is shown as comprised of a pair of porous disk members 70 and 66 which form therebetween the porous arcing chamber 74. The first electrode 44 is secured to the upper porous disk 70 by means of the rivet 48 which also contacts the upper plate 30 as hereinbefore described. The lower electrode 46 is similarly secured to the lower porous disk 66 by means of rivet 50 which, as previously described, also provides electrical contact with the electrode 62, shown in FIG. 6, of the coil shunting gap. While FIG. 5 substantially shows the present preferred embodiment of the upper gap, and also of the lower gap between porous blocks 68 and 72 which is substantially identical thereto, it is to be understood that the particular shape of the arcing chamber 74 and the shape of the electrodes 4 and 46 may be changed, if desired, without substantially changing the desired function of the electrodes and the arcing chamber. As shown in FIGS. 3 and 5, electrodes 44 and 46 are formed of an annular shape such that when an arc is caused to form between their adjacent surfaces, more clearly indicated in FIG. 3, the current within electrodes 44 and 46 will be caused to flow around the opening formed in the electrodes from the rivet 48 toward the rivet 50, forming a current loop, as indicated by the dot-dash line of FIG. 3. In this manner, an electrical flux will be generated between the electrodes which will thereby cause the arc, which is established between such electrodes, to move out along the inner surfaces of such electrodes and into the arcing chamber 74. The slot-s 45 and 47 in electrodes 44 and 46, respectively, prevent circulating or reverse current in the electrodes, which would prevent movement of the are into the arcing chamber.

In a similar manner, the are which is struck between electrodes 58 and 62 in the coil shunting gap (FIG. 6) will provide a local current loop which will cause the are that is formed therebetween to similarly move out into the arcing chamber 64. As previously mentioned, as the arc moves out into the arcing chamber the voltage of such are is substantially increased whereby the current will be caused to flow into the coil 42, inasmuch as the coil 42 provides a smaller impedance than the coil shunting gap after the arc voltage of the gap has been developed. Of course, as the current begins to flow within the coil 42, a flux is set up which will cause thearc within the main gap, formed by the electrodes 44 and 46 and also the arc in the lower main gap, as well as the arc in the coil shunting gap, to move out into their respective arcing chambers, whereby the voltage in such arcs is substantially increased due to the porous material forming the arcing chambers.

It will of course be understood that the lower arcing chamber of the lower main gap, which is formed between the porous plate 68, which forms the bottom portion of the coil. shunting gap chamber, and porous plate 72 is substantially identical to the construction shown in FIG. 5 of the upper main gap.

From FIGS. 4, 5, and 6 it will be apparent that the various porous blocks 70, 66, 68, and 72 of the spark gap assembly 24 fit together in an inter-locking manner to provide an efiicient spark gap assembly of minimum size. Of course, it will be understood that the spark gap assembly may be providedwith any desired number of spark gap structures, the number varying according to the, rating of the arrester with which it is to be used. While a novel lightning arrester, a novel gap structure and a novel gap assembly have been disclosed herein, it will be apparent that the novel gap structure may find utility in other types of protective devices.

From the above description of the present preferred embodiment of the porous gap structure and the coil shunting gap of this invention, it is believed clear that there has been shown and described the invention and the manner in which it is best performed. However, it will be understood that various changes may be made in the constructional details of the invention, such as the particular shape of the arcing chamber and the configuration of the various electrodes without departing from the spirit of the invention hereinbefore set forth. Therefore, while there has been shown and described the particular preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention hereinbefore set forth. All such changes are considered as part of the invention which fall within the scope of the claims appended hereto.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A lightning arrester comprising a tubular housing of insulating material, a metallic terminal at one end of said housing, a second metallic terminal at the opposite end of said housing, a spark gap assembly and non-linear resistantvalve material positioned within said housing and electrically connected to each other, one end of said spark gap assembly being electrically connected to one terminal of said housing, one end of said non-linear valve material electrically connected to another terminal of said housing, said spark gap assembly comprising a plurality of arc interrupting chambers, each chamber having connected thereto a pair of separated electrodes, each arc interrupting chamber being formed of a porous material, one pair of said electrodes being connected in parallel circuit relation with a coil member which is mounted about a porous block forming the arcing chamber for such pair of electrodes, said coil when energized providing a flux for moving an are formed between each pair of electrodes into each one of said plurality of arc chambers, said electrodes in parallel with said coil comprising a shunt means for limiting the voltage across said coil, and transferring current to said coil. V

2. A lightning arrester comprising a housing of insulated material having a metallic terminal at one end of said housing and a second metallic terminal at the opposite end of said housing, a spark gap assembly mounted within said housing, a non-linear resistant material mounted within said housing, one end of said spark gap assembly being electrically connected to one end of said non-linear resistant material, the opposite end of said spark gap assembly being electrically connected to one terminal of said housing, the other end of said non-linear resistant material being connected to the other terminal of said housing, said spark gap assembly comprising a plurality of arcing chambers, each chamber being provided with a pair of separated electrodes mounted in a portion of the arcing chamber, each said pair of electrodes forming an arc gap, said plurality of arcing chambers being formed of porous material, a coil member mounted about a porous block forming one of said arcing chambers, the pair of electrodes mounted in a portion of said one arcing chamber being connected in electrical parallel relationship with said coil member, said coil member when energized providing a flux field for moving the are formed between each said pair of electrodes into said plurality of arcing chambers, said one pair of electrodes in parallel relationship with said coil member acting as a shunt for said coil limiting the voltage across said coil, and transferring current to said coil.

3. A porous gap structure for a lightning arrester comprising a pair of porous blocks inter-fitting with each other and forming therebetween an arcing chamber, a pair of electrodes mounted between said blocks and extending into said arcing chamber, a coil member mounted about said inter-fitting porous blocks, one end of said coil being electrically connected to one of said electrodes, the other end of said coil being electrically connected to the other of said electrodes, said electrodes acting as a shunt for said coil limiting the voltage across said coil, said electrodes being formed to provide a current coil loop in each said electrode, whereby an are formed between said electrode will be caused to move from said point of initial arcing by action of said current loop.

4. A coil and coil shunting gap structure for an electrical protective device comprising a pair of blocks of porous material fitting together to form threbetween an arcing chamber, a pair of electrodes mounted between said blocks and extending into said arcing chamber, sad electrodes forming an arc gap, a coil surrounding at least one of said blocks, one end of said coil electrically connected to one of said pair of electrodes, the other end of said coil electrically connected to the other of said pairs of electrodes, said are gap acting as a shunt for said coil and transferring current to said coil, said porous material acting on an are formed in said are gap to increase the arc voltage of such are.

5. A porous gap structure for a lightning arrester comprising in combination, a plurality of blocks of porous material, each pair of blocks of porous material forming therebetween an arcing chamber, one of said blocks of porous material having mounted thereabout an electromagnetic coil structure, each of said arcing chambers having mounted therein a pair of electrode members, said electrode members being of an annular shape to provide a current loop therein, whereby an are initially formed between said electrodes will be caused to move from the point of initial formation due to said current loop, said coil when energized acting to provide a flux for moving said are further along said electrodes and into said arcing chamber, one pair of electrodes being connected in parallel shunt relationship with said coil member for limiting the voltage across said coil, and transferring current to said coil.

6. A porous gap structure for a lightning arrester comprising in combination, a plurality of blocks of porous material, said blocks of porous material forming therebetween an arcing chamber, one of said blocks of porous material having mounted thereabout an electromagnetic coil structure, each of said arcing chambers having mounted therein a pair of electrode members, said electrode members being formed to provide a current loop therein, whereby an arc initially formed between a pair of said electrodes will be caused to move from the point of initial formation due to said current loop, said coil acting to provide a flux for moving said arc along said electrodes and into said arcing chamber, one pair of electrodes being connected in parallel shunt relationship with said coil member for protecting said coil and transferring current to said coil.

7. A spark gap assembly comprising in combination a plurality of blocks of porous material, are chambers formed between each pair of said porous blocks, terminal means on the upper block of said plurality of porous blocks, second terminal means on the lower block of said plurality of porous blocks, a pair of separated electrodes mounted in each of said arcing chambers, a first electrode of the first pair of electrodes being electrically connected to the terminal means on the upper porous block, one electrode of the last pair of electrodes being electrically connected to the terminal means on the lower porous block, the other electrode of said first pair being electrically connected to one electrode of the next lower pair, the other electrode of the last pair being electrically connected to one electrode of the next higher pair of electrodes, said arcing chambers being formed in said porous material acting to increase the voltage of the are drawn between said pair of electrodes mounted in each arcing chamber, a coil member mounted about said porous block assembly and electrically connected between a pair of electrodes in one chamber, said coil acting to move the are between said pair of electrodes into said arcing chambers, said pair of electrodes connected in parallel with said coil to limit voltage on said coil.

8. A spark gap assembly as claimed in claim 7 in which said electrodes are formed to provide a current loop in each said pair of electrodes whereby an are formed between each said pair of electrodes will be caused to move along said electrodes.

9. A spark gap assembly comprising in combination a plurality of blocks of porous material, arcing chambers formed between pairs of said porous blocks, terminal means on the upper block of said plurality of porous 9 blocks, second terminal means on the lower block of said plurality of porous blocks, a pair of separated electrodes mounted between each said pairs of porous blocks and extending into said arcing chambers, the first electrode of the first pair of electrodes being electrically connected to the terminal means on the upper porous block, one electrode of the last pair of electrodes being electrically connected to the terminal means on the lower porous block, the other electrode of said first pair being electrically connected to one electrode of the next lower pair, the other electrode of the last pair being electrically connected to one electrode of the next higher pair of electrodes, each of the electrodes of the remaining pairs of electrodes being electrically connected to one electrode of another pair of electrodes, said arcing chambers being formed in said porous material acting to increase the voltage of the are drawn between said pair of electrodes mounted in each arcing chamber, a coil member mounted about said porous block assembly and electrically connected between a pair of electrodes in one chamber, said References Cited in the file of this patent UNITED STATES PATENTS 2,000,719 Slepian et al. May 7, 1935 2,772,334 Latour Nov. 27, 1956 2,783,336 Latour Feb. 26, 1957 2,825,008 Kalb Feb. 25, 1958 2,917,662 Cunningham Dec. 15, 1959 3,019,367 Kalb Jan. 30, 1962 3,069,589 Cunningham Dec. 16, 1962 

1. A LIGHTNING ARRESTER COMPRISING A TUBULAR HOUSING OF INSULATING MATERIAL, A METALLIC TERMINAL AT ONE END OF SAID HOUSING, A SECOND METALLIC TERMINAL AT THE OPPOSITE END OF SAID HOUSING, A SPARK GAP ASSEMBLY AND NON-LINEAR RESISTANT VALVE MATERIAL POSITIONED WITHIN SAID HOUSING AND ELECTRICALLY CONNECTED TO EACH OTHER, ONE END OF SAID SPARK GAP ASSEMBLY BEING ELECTRICALLY CONNECTED TO ONE TERMINAL OF SAID HOUSING, ONE END OF SAID NON-LINEAR VALVE MATERIAL ELECTRICALLY CONNECTED TO ANOTHER TERMINAL OF SAID HOUSING, SAID SPARK GAP ASSEMBLY COMPRISING A PLURALITY OF ARC INTERRUPTING CHAMBERS, EACH CHAMBER HAVING CONNECTED THERETO A PAIR OF SEPARATED ELECTRODES, EACH ARC INTERRUPTING CHAMBER BEING FORMED OF A POROUS MATERIAL, ONE PAIR OF SAID ELECTRODES BEING CONNECTED IN PARALLEL CIRCUIT RELATION WITH A COIL MEMBER WHICH IS MOUNTED ABOUT A POROUS BLOCK FORMING THE ARCING CHAMBER FOR SUCH PAIR OF ELECTRODES, SAID COIL WHEN ENERGIZED PROVIDING A FLUX FOR MOVING AN ARC FORMED BETWEEN EACH PAIR OF ELECTRODES INTO EACH ONE OF SAID PLUARLITY OF ARC CHAMBERS, SAID ELECTRODES IN PARALLEL WITH SAID COIL COMPRISING A SHUNT MEANS FOR LIMITING THE VOLTAGE ACROSS SAID COIL, AND TRANSFERRING CURRENT TO SAID COIL. 